Air conditioning apparatus are equipped with various types of devices such as a compressor and a fan. A motor is often used as the source of power for these devices. The motor is connected to a motor drive unit (called a “driver” below) comprising plural switching elements and can be rotated by a drive voltage that is outputted as a result of each of the switching elements in the driver switching ON and OFF.
Further, sometimes the rotational speed of the motor is controlled to allow the various types of devices such as the compressor and the fan to operate in appropriate states. A motor current that is passed through the motor is often used for such motor rotational speed control. Here, as a method of detecting the motor current, for example, as disclosed in Japanese Patent Publication No. 2005-192358, there is known a technology where a shunt resistor serving as a current detection-use element is connected in series on a wire on which the motor current flows and where the motor current is detected on the basis of both end voltages of the shunt resistor.